V8 Throttle Pot Voltages on Oscilloscope (Video!)

[Barkychoc]

I've been meaning to check my throttle pot for a while, anyway I made a little video, here you go, click the image.

Edited by Barkychoc on Friday 29th April 17:20

[ketvrin]

Can you get the bonnet shut with that thing in place Chris

sorry...

K

[Oldred_V8S]

Chris

That looks useful

I will dust my old scope off in case I require it.

Cheers

Paul

[GreenV8S]

Isn't that Voltage a bit high for idle?

[Barkychoc]

I set it according to this Pete - I'm sure an extra 100th of a volt isn't too significant?! The meter probably isn't that accurate anyway - only a cheapo from Maplin.

Edited to add the link

http://www.v8wizard.com/Setting_Air_Mass_Flow_Mete...

Edited by Barkychoc on Saturday 30th April 17:24

[ketvrin]

I don't suppose you have a wiring diagram for a Test rig Chris ?

I have several TP,s but don't know for sure if they are all good
So I would like to test them on the bench. I don't have an Osc.
But do have a good volt meter

I'm obviously talking V6 but I guess the circuit to test would be the same?

K

[Barkychoc]

I'll post something up shortly Kev, it would be really easy.
A digital multimeter is really no good for seeing a noisy output though, an analog needle type meter would be better, do you have any old AVO meters kicking about where you work?

[Alan Kee]

Nice piece, but beware of spindle wear skewing your readings when the engine is running. i only check the voltages at the ECU plug with the engine running, after all that's how the ECU sees it.

[ketvrin]

Barkychoc said:

I'll post something up shortly Kev, it would be really easy.
A digital multimeter is really no good for seeing a noisy output though, an analog needle type meter would be better, do you have any old AVO meters kicking about where you work?

Thanks Chris, I have an old needle analogue multimeter as well somewhere... (its retired). I'll dig it out and use it when I get your guidance

K

[Barkychoc]

Kev - I am working from the circuit diagrams and we are talking TVR here.

You do need to use an analog meter - you can't see voltage flickering on a digital meter, or alternatively an oscilloscope.

Connect Brown wire to power earth and meter black -

Connect Brown/Black to Power (12v will do - it probably runs off less in the system but for this its not critical)

Connect Brown/Green to meter red +

As you turn the throttle pot the voltage should increase on the meter.
Set the meter to DC Volts that will measure up to 12v, so probably 20v range or similar.
Pay attention to the very early part of the throttle pot - the initial movement - as that is likely to be where any wear is.

If you haven't got a handy 12v power source try the meter on the ohms range, you'll have to experiment with the ranges.
black - probe to Brown wire
red + probe to Brown/Green, don't connect brown/black

If there is a break in the track there is a chance you could miss it this way.

I don't even know what the Ford throttle pot looks like so this is all a bit blind.

If anyone has a little briefcase generator I could bring my oscilloscope to Chatsworth

[Oldred_V8S]

Barkychoc said:

Kev - I am working from the circuit diagrams and we are talking TVR here.

You do need to use an analog meter - you can't see voltage flickering on a digital meter, or alternatively an oscilloscope.

Connect Brown wire to power earth and meter black -

Connect Brown/Black to Power (12v will do - it probably runs off less in the system but for this its not critical)

Connect Brown/Green to meter red +

As you turn the throttle pot the voltage should increase on the meter.
Set the meter to DC Volts that will measure up to 12v, so probably 20v range or similar.
Pay attention to the very early part of the throttle pot - the initial movement - as that is likely to be where any wear is.

If you haven't got a handy 12v power source try the meter on the ohms range, you'll have to experiment with the ranges.
black - probe to Brown wire
red + probe to Brown/Green, don't connect brown/black

If there is a break in the track there is a chance you could miss it this way.

I don't even know what the Ford throttle pot looks like so this is all a bit blind.

If anyone has a little briefcase generator I could bring my oscilloscope to Chatsworth

Chris

How did you connect the scope?

[Barkychoc]

I stuck bits of wire into the connector and clipped the scope probe to that. I stuck the meter probes into the connector on the throttle pot side - you can slip them down the sides of the wires.

For clarity this applies to the V8 - the info for Kevin above is for the V6.

[ketvrin]

Barkychoc said:

Kev - I am working from the circuit diagrams and we are talking TVR here.

You do need to use an analog meter - you can't see voltage flickering on a digital meter, or alternatively an oscilloscope.

Connect Brown wire to power earth and meter black -

Connect Brown/Black to Power (12v will do - it probably runs off less in the system but for this its not critical)

Connect Brown/Green to meter red +

As you turn the throttle pot the voltage should increase on the meter.
Set the meter to DC Volts that will measure up to 12v, so probably 20v range or similar.
Pay attention to the very early part of the throttle pot - the initial movement - as that is likely to be where any wear is.

If you haven't got a handy 12v power source try the meter on the ohms range, you'll have to experiment with the ranges.
black - probe to Brown wire
red + probe to Brown/Green, don't connect brown/black

If there is a break in the track there is a chance you could miss it this way.

I don't even know what the Ford throttle pot looks like so this is all a bit blind.

If anyone has a little briefcase generator I could bring my oscilloscope to Chatsworth

Thanks Chris...
I wired an old one I have been carrying as a spare, the way
You say, but I saw 12v at rest, decreasing to almost zero when rotated to around 90 deg ?
Clearly I'm doing something wrong?
The other thing is that when the throttle is fully closed, the TPS is already rotated
To around 16 degrees. Does anyone know what voltages I should see at what angles/postions?

Thanks

K

[Barkychoc]

Kevin if you want the voltage to increase reverse the brown and brown/black wires, but to be honest its not important for testing purposes - as long as the voltage is stable all the way up and down the scale - any flickering of the needle spells trouble.

If you test the one on the car and the voltage goes down with increasing throttle then its the two outer connectors that are the wrong way round on the throttle pot - as recently discussed I think in one of Normans threads.